Who Shot Thebarman will carry Glen Boss' hopes of a fourth Melbourne Cup win but the champion jockey fears the favourite Admire Rakti could blow away his rivals.

"Admire Rakti, I reckon could possibly go out there and win by three or four lengths," Boss said on the eve of Tuesday's famous race at Flemington.

"He's an outstanding stayer. He could blow us all away."

Admire Rakti won the Caulfield Cup with a barnstorming finish under top weight of 58kg and will again be ridden by Hong Kong-based Australian Zac Purton on Tuesday.

Admire Rakti was given a 0.5kg penalty for his Caulfield Cup win, taking his weight to 58.5kg for the 3200m feature.

Boss will forever be linked to Makybe Diva - the champion mare he rode to three Melbourne Cup wins from 2003 to 2005.

Lightly raced Who Shot Thebarman won this year's Auckland Cup over 3200m and has been in the care of premier Sydney trainer Chris Waller for his Melbourne Cup campaign.

Who Shot Thebarman, one of three Cup runners for Waller, is a $17 chance with Admire Rakti the $5 favourite.

"Two things are the key for him - the track and the two miles," Boss said of Who Shot Thebarman.

"He's so much better on bigger tracks like Flemington.

"He was hopeless around Caulfield the other day so if you take that away his form is pretty solid. Whether he's got the class to win one, I'm not sure, but he's certainly going to run the trip to give himself every opportunity."